SUPPLEMENT TO THE BIVALVIA. 19 
2. Cycias TumipuLA, S. Wood. ‘Tab. B, fig. 4 a, 6. 
Cycias Extcua? S. Wood. Lond. Geol. Journ., p. 118, 1847. 
Spec. Char. C. Testéd minimd, ventricosd, tenui, ovato-transversd, subequilaterali, 
levigatd, glabra, anticée rotundatd, obtusd, posticée angustiore et lutiore ; umbonibus 
minimis, viv prominentibus, parum obliquis. 
Length, 3th of an inch; hezght, =3;ths of an inch. 
Locality. Ueadon Hill (S. Wood). 
The shell which I have here called ¢wmédula appears to be more inflated than any other 
known to me. It is very smooth and glossy, with a short dorsal margin, the umbo 
slightly prominent, and the shell is nearly equilateral. It resembles from descriptions 
and figures two or three other species, viz., Ist Cyclas Verneuilli de Boissy, ‘ Mém. de la 
Soc. Géol. de France,’ 2nd ser., t. ii, p. 270, pl. 5, fig. 5; figured also by M. 
Deshayes, ‘ An sans Vert. du Bas. de Par., pl. 34, figs. 40—42, but that shell does not 
appear so tumid as ours. 2nd. Spheriuvm castrense, Moulet, which has been figured 
and described by Sandberger, ‘ Land- und Siissw.-Conch.,’ p. 221, tab. xiii, fig. 1, but this 
also appears less tumid and more transverse than my shell. 3rd. Cyclas elegans, Gould, 
‘Inv. Massach.,’ p. 74, fig. 55, a recent species from the north-east coast of America. 
This latter approaches near to our Headon Hill shell, but is also less tumid. TI have not 
been able to see the interior of my sheil, but it seems to differ from C. Bristoviz in being 
more tumid and equilateral. 
In the year 1843 I found in the truly freshwater bed at Hordle a very small 
specimen of a shell belonging to this genus, to which I gave the name of Cyclas exigua in 
the ‘London Geol. Jour. Mr. Edwards not having in his cabinet a corresponding 
specimen, I gave him the one referred to under this name of eaigua, but I have not 
been able to detect it in his collection now in the British Museum so as to determine 
whether it be the same as that now figured as ¢wmidula, but to prevent confusion I 
have, under the circumstance of the shell apparently not having been preserved by 
Mr. Edwards, given it as the same as twmidula. 
